Drilling in deviated and horizontal sections of a borehole can cause various problems with slime/sediment accumulation, resistance, and wear. When drilling in greatly inclined sections (e.g., over 65 degrees), for example, drilling mud moves along the top of the borehole above the drillpipe, but the mud fails to transport the slime and sedimentation accumulated on the borehole's lower wall. This type of accumulation also develops when drilling in horizontal sections, especially when the drilling tool operates in a “sliding” mode while correcting the well trajectory.
In addition, the tool joints between pipe sections on the drill string experience resistance against the slime/sediment accumulation when the drill string is moved in the borehole. “Cake” can quickly form at the tool joints as slime/sediment fills in at the joints. This quick caking process may cause hydraulic impact that affects the stability of the borehole walls. Although some of the caked slime/sediment may be dislodged by the mechanical rotation and movement of the drillpipe, full slime removal does not occur. Furthermore, the drillpipe's tool joints can significantly contact the borehole walls in a deviated or horizontal section, causing the joints to experience wear when the drillpipe rotates or moves.
There are steel drillpipes in the prior art that have grooves to reduce the drillpipe's contact with the borehole's wall. Examples of such steel drillpipes are disclosed in A. I. Bulatov, S. V. Dolgov, “Driller's Guide,” Moscow, Nedra, 2006, v. 1, p. 153, FIG. 8.8 and in U.S. Pat. No. 4,460,202. Steel drill collars in the prior art may also have grooves, such as disclosed in U.S. Pat. No. 6,012,744. These steel drillpipes and collars, however, can have limited use for drilling highly deviated or horizontal sections of a borehole because the pipe's weight creates high pressing loads that cause higher friction forces while the drillpipe/collar is moving and rotating in the borehole. In addition, the grooves are formed by milling on the outer surface of the steel and are shallow. Grooves machined in this manner do not effectively detach slime/sediment settled on the lower borehole wall.